High voltage low temperature resistance device



Dec. 24, 1968 M. OHANIAN 3,418,620

HIGH VOLTAGE LOW TEMPERATURE RESISTANCE DEVICE Filed May 19, 1966Michael Ohoni INVENT My? VW W WZ Zyef United States Patent 3,418,620HIGH VOLTAGE LQW TEMPERATURE RESISTANCE DEVICE Michael Ohanian, Methuen,Mass., assignor, by mesne assignments, to the United States of Americaas represented by the Secretary of the Army Filed May 19, 1966, Ser. No.551,864 2 Claims. (Cl. 338-57) ABSTRACT OF THE DISCLOSURE A compact highvoltage, high wattage and low temperature coeflicient resistor that ismade by depositing a metallic film or smoke on a piece of glass tubing.The tubing is surrounded by a dielectric and is centrally positionedinside an epoxy glass tube by two end caps that have a series of holesfor passing a high heat transfer and high dielectric strength fluid.

This invention relates to a resistance device and more specifically to acompact high voltage, high wattage and low temperature coeflicientresistor.

Very high values of resistance are made by depositing a metallic film orsmoke on a piece of glass tubing and attaching suitable terminals to theend of the tube. Also, various forms of carbon are used quiteextensively. However, the watt-dissipating capacity of a compactresistor of this type is rather limited, and the value of resistancechanges considerably with the temperature and with impressed voltage.

It is, therefore, an object of this invention to provide a compacthigh-wattage dissipating resistor.

It is another object of this invention to provide an extremely stableresistor for high voltage applications.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconjunction with the accompanying drawing in which the single figure isa perspective view partially in section of a resistance device accordingto the present invention.

Referring now to the figure, there is shown a resistor blank which is astandard metallic film resistor similar to the RN80 series which hasbeen calibrated to the desired ohmic value by selectively cutting aspiral in the film leaving a spiral metallic film 7 about a glass tube9. Electrical connection leads 11 and 13 are fused to the ends of theresistor in a normal manner, and a thick coating of dielectric 15 isapplied over the entire body of the resistor which protects theresistive film from outside elements and still allows satisfactory heattransfer. One example of a suitable dielectric is a one-mil thick epoxycoating per Raytheon specifications S296MS471, paragraph 4.3.2 which hasa dielectric strength of 1500 VDC-per-mil. The resistor is inserted in atube 17 made of epoxy glass and inclosed at each end by caps 19 and 21bonded to tube 17 and the ends of the resistor through which leads 11and 13 extend respectively supporting the resistor symmetrically withintube 17 forming a passageway for fluid communication about the resistor.Each of the caps 19 and 21 have a plurality of apertures 23 disposed ina circular pattern in said caps 19 and 21 coincident with the fluidpassageway inside tube 17 to allow free passage of a suitable high heattransfer and high dielectric strength fluid. Fluids such as FC- andFreon 114 have these characteristics and, therefore, are suitable foruse in the resistor described above.

An RN resistor which is rated at two watts in military specificationswas able to dissipate thirty-eight watts of power with no ill-effectsafter prolonged periods. Higher voltages resulting in more powerdissipation are possible by increasing the distance between spiralturns, resulting in a higher volts per turn rating.

The use of the present resistance device in conjunction with Freon 114or equivalent allows the design of a compact high voltage power supplyor extremely stable resistive load boxes, and the use of epoxy glass fortube 17 allows the resistor to be clip mounted.

It is, therefore, obvious from the above disclosure that the resistancedevice of the instant disclosure is capable of dissipating abnormallyhigh wattage at high voltages using presently available types ofresistor blanks.

While the invention has been described with reference to a preferredembodiment thereof, it will be apparent that various modifications andother embodiments thereof will occur to those skilled in the art withinthe scope of the invention. Accordingly, it is desired that the scope ofthe invention be limited only by the appended claims.

What is claimed is:

1. A high voltage, low temperature resistance device comprising: aresistor blank having electrical connections fused to each end; an innerglass tube; said resistor blank being a metallic film resistor woundaround said inner glass tube and calibrated to a desired ohmic value,said metallic film resistor having a dielectric coating disposed overthe entire outer portion thereof to protect said resistor; a cylindricalhousing comprising a glass tube, said glass tube having end caps bondedto each end thereof through which said electrical connections extendoutward therefrom, said end caps further being bonded to said resistorblank for spacing said resistor blank symmetrically within said glasstube and providing a passageway for a cooling fluid, said end caps eachhaving a plurality of apertures disposed in a circular pattern thereinand coincident with said fluid passageway for allowing free passage of ahigh heat transfer, high dielectric strength fluid.

2. A high voltage, low temperature resistance device as set forth inclaim 1 wherein said glass tube of said cylindrical housing is made ofan epoxy glass for reinforcing said tube whereby said resistance devicemay be clip mounted.

References Cited UNITED STATES PATENTS 1,694,178 12/1928 Hudson 338-571,841,332 1/1932 Kranz 33857 2,338,531 1/1944 Naumann et al. 338-532,381,724 8/1945 Crosby 33857 2,423,021 6/ 1947 Henckler et al. 33857CARL D. QUARFORTH, Primary Examiner. R. L. GRUDZIECKI, AssistantExaminer.

US. Cl. X.R. 33853

